Leeds U.S. Pat. Nos. 2,777,824 and 3,055,297 disclose marking structures made of highly porous plastic material, the pores of which are of microscopic proportions and are filled with a marking fluid such as an ink. Structures made in accordance with the teachings of the Leeds patents have experienced a high degree of commercial success as hand stamps, stamp pads, and also as ink rolls such as are used for applying ink to printing members in automatic printing equipment. Such structures are advantageous because of their long life, both in length of time and in numbers of operations or impressions, and because they operate well without the necessity of repetitive re-inking of the marking surface.
One problem with the method of making the marking structures disclosed in Leeds U.S. Pat. Nos. 2,777,824 and 3,055,297, is the time required to produce these structures. For example, in the case of hand stamps, the total processing time may be a period on the order of about 15 hours. A lengthy period of time is primarily required for a stabilization step in which the molded structure reaches an initial dimensional stability and excess ink flow from the structure is stabilized. One solution to this problem is to use an absorbent backing during molding that absorbs excess ink and thereby eliminates the need for a lengthy stabilizing step. See Ooms et al. U.S. Pat. Nos. 4,927,695 and 5,049,432, the contents of which are incorporated by reference herein.
However, a concern with the marking structures made using the disclosures of Leeds and Ooms et al. is that the process is complex and requires skilled workers and specialized equipment to produce acceptable marking devices. Known methods of making marking structures generally involve an initial step of making a mold having indentations or cavities corresponding to a relief pattern to appear on the marking structure. The mold, or matrix board, is essentially a flat plate having a rectangular indentation on one side.
Currently, premix molding requires a complicated, high-priced, machined metal chase, consisting of a bottom plate, middle frame, some of which have excess premix overflow channels, and a lid. The matrix board is put between the middle frame and bottom plate. Premix is poured onto the matrix board. The middle frame of the lid keeps the liquid premix from running out. The lid goes on top, and then the entire assembly is put into a heated press for molding. The overflow channels on the middle frame aid in draining of excess premix during the molding cycle. Before a new casting is made, the chase needs to be disassembled and cleaned using cleaning chemicals that are potentially damaging to the environment. This is a time consuming, messy operation. Often, the solvents used also present a fire hazard.
The present invention provides a molding method which addresses these problems by providing an alternative to the use of a molding chase.